Barnes & Noble (BKS) offers a special $20 gift card to customers who buy a Nook HD or Nook...

Barnes & Noble (BKS) offers a special $20 gift card to customers who buy a Nook HD or Nook HD+ between now and Monday using their MasterCard card. Though it's a small and limited offer, the company is on the radar of investors for any signs that unit sales growth is slowing.